The majority of world wind farms use three-bladed horizontal-axis aero-generators. Nevertheless, there is a large number of low-power air-pumps and aero-generators that make up a very small part (of little importance) of total installations.
As for the general size, there are different levels of technological maturity. The dimensions of aero-generators have been increasing, gradually increasing from 75 kW, 15 m-diameter aero-generators to 40–65 m diameter and 500–1500 nominal kW machines, all with three blades to windward and a tubular tower to leeward. During the development of the technology there have been no major innovations. The process has consisted of optimizing and improving designs and manufacturing processes, resulting in an improvement in the availability of the aero-generator, in production yield, in a reduction in specific weights (Specific Weight [Weight=rotor+gondola]/rotor swept area), in a reduction in installation, operation and maintenance costs but always keeping the same structural parameters (Height of tower=¾ diameter of rotor+10 in meters).
To be more specific, the current systems are:                Three-bladed aero-generators with regulation for aerodynamic loss with two-speed rotation via the normal system of connecting poles in asynchronous generators.        Three-bladed aero-generators with regulation for aerodynamic loss with fixed-speed asynchronous generators.        Three-bladed aero-generators with regulation for change of wind, combined with a small-range variable speed system (Opti-slip).        Regulation systems for change of wind at fixed speeds.        Three-bladed aero-generators with no multiplication box through multi-poled synchronous generators, regulated for change of wind and variable speed system.        
The aero-generator is generally three-bladed with a tubular tower to leeward, regulated for loss and/or change of wind and an active orientation system. The rotor activates a multiplier, which in turn activates the generator; a brake disc is placed on the exit axis of the multiplier.
Despite the confirmed good functioning in generating and using wind, structurally there are various problems due to the shadow of the towers on the blades, the gyroscopic moments created because the center of gravity of the rotor is displaced with respect to the rotation axis, specific weights in the order of 14 kg/m2 and the pitching moments due to constant changes in wind direction and differences in speed between the upper and lower blades, which have an effect on the whole structure, weakening it when endowed with rigid rotors, as well as the inconvenience of assembly and maintenance at high altitudes.
It is important to highlight the increase in specific weight in large aero-generators. If we compare values of aero-generators of 45 m in diameter (600 kW of nominal power) and 60 m in diameter (1 MW of nominal power), there is an increase of more than 30%, which has an effect on the specific cost (total cost/area swept) as well as a 35% increase in the costs of the installed kW. Below we will describe some of the basic components:
Rotor: The rotor generally has three blades, with a bushing that is fixed to the axis that is embedded on two bearings fastened tightly to the gondola chassis, or is placed directly onto the multiplier entrance axis. The rotors used are usually slow rotors with speeds at the end of the blades of 55 m/s, their rotation level being five meters from the column of the axis they pivot on, and produce gyroscopic effects that tend to destabilize the machine. In most cases, the rotor is situated windward of the tower (front wind). This has the advantage of reducing wind stress on the blades by minimizing the shadow effect of the tower and avoiding the aerodynamic noise produced by the blades when they are situated to leeward. Three-bladed aero-generators currently account for 80% of total installations. Nevertheless, as rotor diameter increases, so does the number of two-bladed aero-generators, which are usually designed to be used to leeward and where the shadow effect of the tower on the blades is more noticeable, thus producing significant stresses and vibrations.
Guiding: Most aero-generators use a guiding system using a servomotor that activates the cogs that work on the perforated crown of the gondola coupling with the support tower. This system also has brake discs and pincers that keep it in place when it is positioned. This produces gyroscopic moments and pitching moments due to the constant changes in wind direction, which act through the rotor on the multiplier and the overall structure.
Power control: The power generated is controlled in two ways, due to aerodynamic loss and due to wind change. The latter allows maximum generation in a large range of wind speeds, also having a safety system against high winds (blades in the air), whereas the former needs additional breaking provisions. Wind change controls are equipped with complex moving parts and the corresponding risk of failure and greater maintenance needs.
Tower: As far as the structure of the tower is concerned, the majority are steel vertical, tubular and independent. To optimize the structure, a barrel shape is adopted, the diameter gradually decreasing between the base and the gondola. The height of towers is inconvenient when it comes to assembling and maintaining them. Moreover, the fact that the generator is situated on the gondola, which revolves, results in the problem of how to transmit power to the ground through cables. Until now, most manufacturers have made a loop with the cables to minimize the effect of the coiling resulting from the changes in guiding, which in turn requires a computer operated control system that counts the number of rotations accumulated and orders the gondola to rotate in the opposite direction to uncoil the cables. Even though there has been some gradual technological development in relation to power lines, variable pitch and speed, control systems, material and in other areas, too, perhaps the best results have been obtained with large-scale machines. Specific energy (kWh/m2) increases with the rotor diameter thanks to the increased height of the tower, which is synonymous, in most cases, with increased wind speed. However, increased wind speed may not compensate the increase in manufacturing costs if, keeping current technical design concepts, attempts are made to design machines with diameters larger than the rotor's 50 m. This is due to the fact that the main pressure on aero-generators depends on the cube of the rotor diameter, the weight and manufacturing costs increasing in the same manner, while the increase in energy produced increases with the area of the rotor. On the other hand, specific costs of transportation, assembly, operating and maintenance of these high-power machines are greater than those of aero-generators currently on the market. Making larger competitive machines depends on the development of novel and suitable designs, with the result that there is no significant increase in their specific weight.